Ask too much about rush (10)
I believe the answer is:
overcharge
'ask too much' is the definition.
(I've seen this before)
'about rush' is the wordplay.
'about' becomes 'over' (both can mean around).
'rush' becomes 'charge' (charging is a kind of rushing).
'over'+'charge'='OVERCHARGE'
(Other definitions for overcharge that I've seen before include "Demand too much money" , "Ask too high a price" , "leave phone plugged in unduly long!" , "Rip off" , "Ask too much" .)